Fix Print Preview destinations list sizing breakage

Print Preview's destination dialog is displaying multiple scrollbars
again. Bisected the issue to https://crrev.com/c/1252682 which
recommends adding min-height: 0 to inner nested flexboxes.

Bug: None
Change-Id: I0d33a9cc79c1f74d7f0a2e79fb2e894d47bc38f4
Reviewed-on: https://chromium-review.googlesource.com/c/1260221Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596483}

chrome/browser/resources/print_preview/new/destination_dialog.html

@@ -72,6 +72,7 @@
         display: flex;
         flex: 1;
         flex-direction: column;
+        min-height: 0;
       }
 
       /* Height = 3 * destination item + 10px padding + 1 line text */